CHAPTER VII 



THE DEMONSTRATION OF THE FALL OF SPORES BY MEANS 

 OF A BEAM OF LIGHT 



AFTER I had made the observations upon Polyporus squamosus 

 which have just been described, it occurred to me that it might 

 be possible to see the clouds of spores falling from any hymeno- 

 mycetous fungus with the aid of a sufficiently strong beam of 

 light. Accordingly, a large Horse-mushroom (Psalliota arvensis) 

 was obtained and placed as a cap on an open glass box. The light 

 from an electric arc was allowed to pass through a small hole in 

 a dark screen, and the rays were then collected and turned into 

 a strong parallel beam by means of a biconvex lens. The beam 

 was then directed so that it passed through the glass box. At once 

 a very striking and remarkable result made itself apparent. On 

 looking at the beam of light in the box, one could see the spores 

 floating in the air in countless thousands. It seemed as if, in 

 miniature, a heavy brown-flaked snow-storm was taking place. 

 Curls and wreaths of spores, formed by convection currents, were 

 constantly proceeding from the gills, and the air in the box quickly 

 became densely laden with spores. In the course of a few minutes 

 the density of the spore-cloud in the box became constant. At this 

 stage, doubtless, just as many spores settled on the bottom of the 

 box as were given off at the top by the Mushroom gills. The 

 spores were not to be seen merely as clouds. One could clearly 

 perceive any individual spore floating in the light, and follow its 

 course for some distance. 1 It has thus fallen to my lot, by using 

 a very simple method, to be the first actually to observe the 



1 On the same principle that one can see a star, although it has no appreciable 

 disc, or a spider's web in strong sunlight at a distance of several yards. One does 

 not perceive the dimensions and shape of a spore owing to the insufficient resolv- 

 ing power of the eye. One is simply aware that it sends out light. 



